With an increase in the recording density of magnetic disks, the distance between the magnetic disk serving as a recording medium and the head for use in recording of information or playback has become almost nil close to contact therebetween. The magnetic disk is provided over the surface thereof with a carbon protective film or lubricant film for the purpose of diminishing abrasion due to the contact or sliding of the head thereon or preventing contamination of the disk surface.
The carbon protective film is produced generally by the sputtering process or CVD process. The disk surface is protected with the two films, i.e., the carbon protective film and the lubricant film thereover.
The lubricants generally in use are fluoropolyethers having functional groups. Examples of functional groups are hydroxyl, amino and cyclophosphazene groups. Particularly, lubricants having a phosphazene group are materials having high resistance to decomposition and known as materials for giving high durability to magnetic disks (for example, Patent Literature 1, 2).
The cyclophosphazene group takes the molecular structure of 6-membered ring comprised of three phosphorus atoms and three nitrogen atoms as a main skeleton, and two substituents lengthening up and down of the 6-membered ring from each phosphorus atom (for example, Nonpatent Literature 1). Although the lubricant film on a magnetic disk is required to be thin more and more under the environment wherein the magnetic head is levitated at a low level for a recent rapidly increasing ever-higher recording density, it is difficult to reduce the bulk of molecules of the cyclophosphazene compound.
Patent Literature 1: JP Patent No. 4137447
Patent Literature 2: JP Patent No. 4570622
Nonpatent Literature 1: Tribology letters, 2008, Vol. 31, p 25-35
An object of the present invention is to provide a compound having a reduced bulk of molecules while maintaining excellent resistance to decomposition similar to that shown by phosphazene compound, lubricants comprising the compound, and magnetic disks.